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Does smoke really help in the fight against dengue?

For years, fumigation by civic agencies has been projected as a powerful weapon against dengue. Fogging does indeed kill adult mosquitoes — but in the absence of other, often commonsense measures, it is reduced largely to a spectacle with a limited, short-duration impact.

Written by Naveed Iqbal | New Delhi |
Updated: September 18, 2015 1:55:42 pm
dengue, dengue deaths, dengue in delhi, delhi dengue, delhi govt dengue, delhi dengue deaths, delhi hospital dengue, delhi dengue fogging, delhi dengue awareness, delhi news, health news, NCR news, india news, latest news The fog is a mixture of diesel and a cocktail of insecticides. Top civic medical officials say this ‘high-risk formula’ has only ‘psychological effects’. (Source: Express Photo by Tashi Tobgyal)

The Delhi government’s first response to the dengue outbreak was to step up fogging. After that, it moved to add beds to hospitals to deal with the sudden surge in patients. And finally, it issued a reminder to the public at large to keep surroundings clean.

Healthcare specialists with experience and expertise in tackling the vector-borne disease think the government’s response was “uninformed”. The last response should have come first, the experts say — not just because of the old wisdom about prevention being better than cure, but also because fogging simply “does not work”.

Health Minister Satyendar Jain should have warned citizens to take preventive measures — such as not allowing water to collect inside homes — before summoning the three municipal bodies to point out the lack of fumigation in residential and commercial areas, and to urge them to “increase anti-mosquito drives to prevent dengue”, they say.

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The fogging machines used by the municipal corporations in Delhi spray 95 litres of diesel mixed with insecticides in an hour. The civic bodies procure the insecticides in bulk at the beginning of each financial year, while the diesel is bought as part of their day-to-day expenditure.

Civic officials estimate the rough cost of fogging to be Rs 6,000 per colony per hour. In any particular colony, fogging is carried out once in 10 days, for two hours each in the morning and evening. The cost of a day’s fogging in a colony is, therefore, about Rs 24,000.
This rather expensive fog remains effective in the air for just five minutes. And there are reasons to believe that it does not deliver enough bang for the buck.


dengue, dengue deaths, dengue in delhi, delhi dengue, delhi govt dengue, delhi dengue deaths, delhi hospital dengue, delhi dengue fogging, delhi dengue awareness, delhi news, health news, NCR news, india news, latest news An MCD Fumigation Worker at work in the old quarters of Delhi on Monday. (Source: Express Photo by Tashi Tobgyal)

The civic bodies themselves are clear that fogging does not eliminate the risk of dengue, and that fumigation has “only psychological effects”. Dr SK Seth, Director, Hospital Administration, at the MCD Headquarters told The Indian Express, “Fumigation is not a preventive measure, it is only a containment measure. A high-risk formula with only psychological effects — that is, it makes people feel safer.”

Additionally, Dr Seth said, one of the insecticides used for fumigation, malathion, can be hazardous for humans, especially for vulnerable groups. “It is a very dangerous poison, especially harmful for children, pregnant women, and asthmatics,” Dr Seth said.
The World Health Organisation’s (WHO’s) classification of hazardous insecticides puts malathion as a “Class III” chemical, which is “slightly hazardous”. But Seth explained that inhaling malathion can make the chemical more harmful. “Intake can happen through inhalation and also directly through the skin, and when in the liver, it forms a chemical called malaoxon, which is far more poisonous than malathion itself,” he said.


Dr K Srinath Reddy, president of Public Health Foundation of India, said fogging has not been found to be very effective, and is good only for an “immediate response with no lasting effect”. Since fogging was introduced in 1996, Dr Reddy said, its role has been more to reassure the community than anything else. But that isn’t always a good thing, he said: “It can be used to give a push to efforts as it kills adult mosquitoes, but it is counterproductive because it gives a false sense of security to the public.”

Dr Chittaranjan Behera, Assistant Professor of Forensic Medicine at AIIMS, echoed Dr Reddy. Malathion, he said, is harmful both in the long and short term. In the long term, it can have chronic effects, while in the short term, it can cause breathing problems and headaches in a normal person. It is especially harmful to persons with compromised breathing ability, he said.

Dr Behera also pointed out that while malathion is most effective in closed spaces, civic agencies carry out the bulk of the fogging in open areas. Also, the Aedes mosquito that causes dengue is an indoor, clean-water breeder, and an indoor biter. “Fumigation is not foolproof. Dengue has to be controlled at the larval stage,” he said.

The corporations are aware of the limited effects of fumigation. But several officials said it is still done for the optics — and to satisfy the demands of the public and politicians.


The fogging spray used by the civic bodies contains a mixture of one part malathion (a chemical insecticide) plus pyrethrum (a natural insecticide), and 19 parts diesel. On the use of diesel, the WHO’s guidelines for diagnosis, treatment, prevention and control of dengue state: “Diesel fuel has been used as a carrier for thermal fogging agents, but it creates thick smoke, has a strong smell and creates oily deposits.”

Civic officials do not deny this. They also agree that the chemicals used in the fogging can seep into the soil and contaminate ground water.


With the number of confirmed dengue cases well beyond 1,800, it is unlikely that containment alone will work in Delhi at this stage. According to the WHO, fogging operations will have some success in killing adult mosquitoes in a particular area, but “the residents must be cautioned that this activity alone is not enough to protect everyone or prevent all dengue infections”. In an email to The Indian Express, Dr Arun Thapa, Acting WHO Representative in India, said that any method that reduces the number of infective adult mosquitoes, even for a short time, should reduce transmission of the virus during that time, “but it remains unclear whether the transient impact of space treatments is epidemiologically significant in the long run”.

Preventive measures suggested by the WHO include making sure there are no dengue mosquitoes breeding in discarded tyres, drums, buckets or other water storage containers, and that individuals are protected from mosquito bites both indoors and outdoors during daytime, early mornings and early evenings.

The most effective personal protection comes from applying insect repellant and/or wearing long sleeves and long pants, it says.

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